1. Field of the Invention
The present invention is in the field of day-night viewing devices which can be used both in the day time to obtain a view of a scene, and which can also be used at night or under other conditions of low ambient lighting in order to view such a scene. At night the scene is also intensified or amplified by use of an image intensifier tube to provide a visible image when the scene is too dark to be viewed with diurnal vision. Accordingly, this invention relates to such viewing devices which may be used both in day and at night for observation and surveillance.
The present invention also relates to laser range finding apparatus and method. Such laser range finding apparatus and methods ordinarily project a pulse of laser light into a scene. The laser light pulse illuminates objects in the field of view and is partially reflected from at least one object in the scene whose distance from the observer is to be determined. In order to select this one objects the device may include a reticule and the laser light pulse may be of "pencil beam" configuration corresponding to the reticule. The reflected portion of the laser light pulse is detected at the devices and the transit time for the laser light pulse to travel to and from the object is used to calculate a range to the object using the speed of light as a measuring standard.
2. Related Technology
A conventional day/night telescopic sight is known in accord with U.S. Pat. No. 5,084,780, issued Jan. 28, 1992 to E. A. Phillips The Phillips patent appears to teach a telescopic day/night sight which has several alternative embodiments. According to one embodiment set out in the Phillips patent, such a telescopic sight includes a single objective lens behind which is disposed an angulated dichroic mirror. This mirror divides light coming into the sight via the objective lens into two frequency bands. Light of longer wavelengths (lower frequencies) is allowed to pass through the dichroic mirror to an image intensifier tube. This image intensifier tube operates in the conventional way familiar to those ordinarily knowledgeable about night vision devices. That is, the image intensifier tube provides a visible image which replicates a dim image or an image formed by invisible infrared light within the so-called near infrared. Thus, the longer wavelength band which passed through the dichroic mirror includes the infrared portion of the spectrum, and provides to the image intensifier tube the frequencies of light to which the tube is most responsive.
The visible portion of the light entering the Phillips sight via the objective lens is reflected by the dichroic mirror into an optical system leading to a combiner and to an eyepiece. At the combiner, the image provided by the image intensifier tube is superimposed on the image from the visible-light channel of the sights and the resulting combined image is presented to a user of the sight via the eyepiece.
A possible disadvantage of the Phillips sight as described above is that the angulated dichroic mirror can introduce both parallax, astigmatism, and color aberrations into the image provided to the user. Thus, slight movements of the sight may cause the user to experience some shifting of the image along a line parallel with the angulation of the mirrors while the image does not shift along a line perpendicular to this angulation. In other words such an angulated dichroic mirror may result it the slight jiggling inherent in a hand-held telescope or weapon sight amplifying the apparent movement of the image in at least one direction. This effect can be disconcerting for the user of the device.
Other versions of the Phillips sight use a separate objective lens for both the day channel and the night channel of the sight. These versions would not appear to suffer from the same possible parallax problem described above with respect to the versions using the dichroic mirror. However, the versions of Phillips sight with two objective lenses suffer from an increased size, weights and expense because of the additional optics and larger housing required to mount and protect these optics.
In each case with the sight disclosed by Phillips, the optical channels for the night sight and the day sight are laterally offset relative to one another. These two offset optical channels are parallel, and the image from these channels is combined for presentation at the eyepiece. However, in each case, the sight taught by Phillips requires separate laterally offset optical channels, and presents the problem of correctly and precisely superimposing the image from these two channels for the user of the sight.
Another consideration with the Phillips sight is the mechanism and size of housing required for effecting windage and elevation adjustments of the reticule. Some versions of the Phillips sight use a reticule plate, while others use an injected reticule (i.e., provided by a projector for a lighted reticule "dot" which is superimposed on the image of the viewed scene). In each case, the objective lens of the device receives a larger scene image (i.e., field of view) than is provided to the user, and the reticule is moved about within this field of view in order to provide windage and elevation adjustments. However, it is often desirable for the user of such a sight to perceive no apparent change in the centering of the reticule on the field of view. This results in a smaller imaged field of view with a centered reticule pattern moving about in a larger field of view provided by the objective optics. Understandably, optical systems of this type suffer from increased size and weight because of the larger objective optics.
Yet another disadvantage of sights of this conventional type is that the mechanism for moving the reticule is inherently located near the rear of the sights. This location for the reticule mechanism results in the housing of the sight being undesirably large at a location where clearance must be provided for the action mechanisms of many weapons.
Another conventional day/night weapon sight is known in accord with U.S. Pat. No. 5,035,472, issued Jul. 30, 1991 to Charles L. Hansen. The '472 patent appears to disclose a sighting device including a number of dichroic reflectors, which divide the incoming light into spectral bands. The visible one of the spectral bands passes to an eyepiece for viewing by a user of the device. Another of the spectral bands of light passes to an image intensifier tube. A visible image provided by this image intensifier tube then passes to the eyepiece. Yet another spectral band passes to a focal plane array device, such as to a CCD. The CCD is associated with a display device, such as a CRT. The image from the CRT then passes to the user via the eyepiece.
The device disclosed in the '472 patent appears not to provide laser range finding. No provisions appear to be made for a reticule usable in sighting by use of this device. Focusing and adjustment of a reticule position for windage and elevation also appear not to be addressed by the '472 patent.
Conventional laser range finders have also been known for a considerable time. One exemplary version of such a device is known as the MELIOS. This device uses viewing optics, a laser having a projection optical system, and a detector having a separate receiving optical systems all directed at a scene in which an object is located having a range to be determined. In operation, the laser provides a pulse of laser lights and this is projected into the scene via the projection optics. This laser light illuminates the object, and a portion of the laser light is reflected back toward the device. Part of the reflected laser light returning to the device is captured by the receiving optical system, and is directed to a detector. The device includes a timer starting when the laser light pulse is transmitted and stopping when the returning laser light is detected. A calculator portion of the device uses the elapsed time from transmission of the laser light pulse until detection of the returning reflected laser light to calculate the distance to the object.
Another conventional laser range finder is known as the Commander's Viewer Sight. This device uses a catadioptric optical viewing system, and places separate optics for projecting and detecting the laser light in the central obscuration of the viewing optical system. Thus, the viewing optics and laser range finder optics (i.e., projector and detector optics) are coaxial in this sight, but they are nevertheless separate optical structures.
Still another device which includes a laser and an imaging system responsive to reflected laser light from a scene is known as the TLOS system. This system allows observation of retroreflective optical targets in a scene by projection of a train of laser light pulses and timed operation of an image intensifier tube with a delay interval accounting for imaging objects within a range envelope in the scene. The TLOS device requires use of an optical filter during day time operations, which optical filter passes substantially only the wavelength of light provided by the laser. Pulses of laser light. This optical filter eliminates optical "noise" resulting from light of other wavelengths to which the image intensifier tube is responsive. Such light is rich in the day-time scene. A long standing problem with devices such as the TLOS is that the conventional laser requires temperature stabilization to stabilize the wavelength of laser light projected at the wavelength passed by the optical filter.
In the case of portable devices which are battery operated, such temperature stabilization of a laser light source represents a significant and undesirable energy expenditure requirement.